Mapping the shape of the accretion disk of Hercules X‐1

Leahy, D. A.

doi:10.1002/asna.200310210

Cited by 12 publications

(13 citation statements)

References 17 publications

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“…Low states in the 35‐d cycle of Her X‐1 is generally believed to be composed of the phases in which X‐rays from the neutron star is obscured (Petterson 1975; Scott & Leahy 1999; Scott et al 2000; Leahy 2004). The resultant X‐ray flux for both normal low states and anomalous low states is a combination of scattered and reflected components and has been found to fit well, except for normalizations and excess absorption, to high state spectrum models (e.g.…”

Section: Discussionmentioning

confidence: 99%

X-ray spectral evolution of Her X-1 in a low state and the following short high state

İnam¹,

Baykal²

2005

Monthly Notices of the Royal Astronomical Society

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We analysed spectral variations of ∼8.5‐d long Rossi X‐ray Timing Explorer (RXTE) monitoring observations of Her X‐1 in 2001 December. This set of observations enables, for the first time, frequent continuous monitoring (111 pointings in ∼8.5 d) of the source with RXTE including a ∼1.7‐d‐long low state part and the following ∼6.8‐d‐long short high state part. We used an absorbed power‐law model with an iron line energy complex modelled as a Gaussian to fit both the 3–60 keV Proportional Counter Array–High Energy X‐ray Timing Experiment (PCA–HEXTE) overall short high state spectrum and 3–20 keV individual PCA spectra. An additional partial cold absorber model was used for both cases. Using 3–20 keV individual PCA spectra, absorption in anomalous dips (ADs) and pre‐eclipse dips (PDs) in the short high state was compared. Decreasing the ratio of unabsorbed to absorbed flux with increasing unabsorbed flux in ADs and PDs was interpreted as evidence of the fact that the regions causing opaque obscuration and soft absorption are not geometrically far away from each other. Higher iron line peak energies in the low state and the short high state (∼6.6–6.9 keV) were interpreted as a clue of the presence of iron line components other than the Kα emission line.

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Section: Discussionmentioning

confidence: 99%

X-ray spectral evolution of Her X-1 in a low state and the following short high state

İnam¹,

Baykal²

2005

Monthly Notices of the Royal Astronomical Society

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“…Following the often adopted baseline model of Her X-1 (Katz 1973;Schandl & Meyer 1994;Scott et al 2000;Ketsaris et al 2001;Leahy 2004,and references therein), the ∼12 day long main-on starts when the outer rim of the accretion disk opens the line of sight to the central neutron star (see Fig. 2).…”

Section: Introductionmentioning

confidence: 98%

Probing the outer edge of an accretion disk: a Her X-1 turn-on observed withRXTE

Kuster

Wilms

Staubert

et al. 2005

A&A

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We present the analysis of Rossi X-ray Timing Explorer (RXTE) observations of the turn-on phase of a 35 day cycle of the X-ray binary Her X-1. During the early phases of the turn-on, the energy spectrum is composed of X-rays scattered into the line of sight plus heavily absorbed X-rays. The energy spectra in the 3-17 keV range can be described by a partial covering model, where one of the components is influenced by photoelectric absorption and Thomson scattering in cold material plus an iron emission line at 6.5 keV. In this paper we show the evolution of spectral parameters as well as the evolution of the pulse profile during the turn-on. We describe this evolution using Monte Carlo simulations which self-consistently describe the evolution of the X-ray pulse profile and of the energy spectrum.

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“…The disc consists of a continuous series of tilted rings of increasing radius and warped due to an increase in twist with radius. The line or locus of nodes marks the intersection of the accretion disc with the orbital plane, and it is modelled here by a linear relation between the ring radius ( r ) and the azimuthal angle (φ):

r (ϕ) = R_{normali} + (R_{o} - R_{i}) (ϕ - ϕ_{i}) / Δ ϕ,

where

R_{normali} = 360 \pm 120

km is the inner disc ring radius,

R_{normalo} = 1.6 \times 10^{6}

km is the outer ring radius (Table ),

ϕ_{normali} = 1102

is the inner node's azimuthal coordinate and Δφ = 79°.4 is the reference disc twist angle (Leahy , ).…”

Section: The Accretion Stream–accretion Disc Impact Modelmentioning

confidence: 99%

“…The X‐ray pulse profile shows a strong variation with 35‐d phase (Scott et al ; Leahy ). Extreme Ultra Violet Explorer ( EUVE )/Deep Survey (DS) and Rossi X‐ray Timing Explorer ( RXTE )/All‐Sky Monitor (ASM) observations were used by Leahy (, ) to determine Her X‐1's accretion disc geometry by modelling the X‐ray flux profile as well as the occultation of HZ Her's X‐ray heated side. Leahy & Igna () showed recently that the X‐ray turn‐on does not occur at specific orbital phases in the 1996–2009 Her X‐1 RXTE /ASM light curve.…”

Section: Introductionmentioning

confidence: 99%

“…In this paper, we present the results of modelling the geometry of the HZ Her/Her X‐1 system and accretion stream–accretion disc impact, and compare modelled impact timings with observed light‐curve dip timings. This model is based on Simon et al's () and Leahy's () hypotheses, which was not investigated adequately prior to our study, and focuses on the situation immediately before impact. Our investigation covers, for the first time, the effect of various system parameters on dip timings, accretion disc penetration by the stream, the marching dip effect and several features of the 35‐d phase–orbital phase graph.…”

Section: Introductionmentioning

confidence: 99%

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Light-curve dip production through accretion stream-accretion disc impact in the HZ Her/Her X-1 binary star system

Igna

Leahy

2012

Monthly Notices of the Royal Astronomical Society

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We discuss the production of Hercules X‐1's (Her X‐1) light‐curve dips through accretion stream impact on the disc. We model the binary system geometry, the position of the line of sight relative to the impact site and the effect of several binary system parameters on the occurrence phases of dips. Our input accretion disc models have been validated by observations. The accretion stream geometry is calculated from first principles and it is consistent with theoretical studies and observations. Our model explains the marching dip effect and several other features of the 35‐d phase–orbital phase graph. The outer accretion disc radius has the greatest effect on the timing of dips, while the mass ratio, L1's coordinates, the orbital inclination and separation, and the inner accretion disc radius have negligible effects. We find that dip production occurs for distances from impact to the line of sight of under 2 per cent of the orbital separation. We consider the possibility of disc penetration by the stream and find that it is required to reproduce correctly the marching dip effect and the complex trends of the dips observed by the Rossi X‐ray Timing Explorer/Proportional Counter Array. In particular, the model explains the properties of pre‐eclipse, anomalous, post‐eclipse, main‐high‐state, short‐high‐state and low‐state dips, and shows that they are all produced by the same mechanism.

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Mapping the shape of the accretion disk of Hercules X‐1

Cited by 12 publications

References 17 publications

X-ray spectral evolution of Her X-1 in a low state and the following short high state

X-ray spectral evolution of Her X-1 in a low state and the following short high state

Probing the outer edge of an accretion disk: a Her X-1 turn-on observed withRXTE

Light-curve dip production through accretion stream-accretion disc impact in the HZ Her/Her X-1 binary star system

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